This invention relates to a method of applying a pre-tensioned, metal containment shroud or band by hydraulic or pneumatic means to the rotor of a permanent magnet electrical machine.
In permanent magnet electrical rotating machinery the magnets are frequently positioned in the rotor and held in place against the action of centrifugal force by a band applied over the magnets. The band must have a well controlled residual tension after application in order to prevent radial lift-off of the magnets without exceeding the strength limits of the banding material.
Resin-fiber composite wraps have been used for such bonding with fiberglass or Kevlar.RTM. being the primary strength element and epoxy or polyester resins acting as binders. Some of the problems with this technique are the uncertainty of the residual tension, creep, and temperature limitations of both the fiber and the resin.
Shrunk-on metal shrouds have also been used. They are typically applied to the rotor by heating the metal shroud to a high enough temperature to expand it and provide enough diametral clearance to allow assembly. Too low a temperature rise can cause the shroud to bind on the rotor before the assembly is completed, and too high a temperature can be harmful to the heat treatment of the metal shroud, or can cause demagnetization of the magnets if they have been magnetized. Another problem is that the manufacture of thin walled metal cylinders of the high accuracy required can be expensive.
It is an object of the present invention to assemble metal shrouds onto permanent magnet rotors without heating and with the desired residual stress.
It is a further object of the present invention to produce the final sizing of the retaining shroud before assembly.